This invention relates to a method of reducing the benzaldehyde or benzotrihalide content in a mixture with a compound that boils at about the same temperature. In particular, it relates to adding a benzotrihalide or a benzaldehyde to the mixture to react with the benzaldehyde or a benzotrihalide, respectively, in order to form products having a greater difference in boiling point and therefore are more easily separated by distillation.
When 2,4-dichlorotoluene (2,4-DCT) is reacted with chlorine in the presence of ultraviolet light a mixture of 2,4-dichlorobenzylchloride (2,4-DCBC) and 2,4-dichlorobenzalchloride (2,4-DCBAC) can be made. If the reaction mixture is exposed to moisture, however, some of the 2,4-DCBAC is hydrolyzed to 2,4-dichlorobenzaldehyde (2,4-DCBAL). When the product mixture is distilled, the 2,4-DCBC contains 2,4-DCBAL due to a relative volatility of close to one (boiling points) =248 and 250.degree. C., respectively). The presence of 2,4-DCBAL in the 2,4-DCBC is not acceptable for uses such as making stabilizers, but separation of the 2,4-DCBAL by distillation is time-consuming and costly.
When p-chlorotoluene (PCT) is chlorinated, a mixture of p-chlorobenzalchloride (PCBAC) and p-chlorobenzotrichloride (PCBTC) can be made. Separating the PCBAC by distillation is difficult due to the low relative volatility between PCBAC and PCBTC, reduces distillation yield.